The Molecular and Atomic Gas in IC 342

In addition to the bright CO nuclear peak, there is a prominent CO 2'ï¿½5' bar and an extensive CO disk. The bar and nucleus contain 30% of the total observed CO emission in IC 342. Beyond the bar the CO disk contains two spiral arms, which coincide with the two inner optical arms. The substantial interarm CO component within this inner region has a mean surface density of 8 Msolar pc-2, close to the mean surface density of 10 Msolar pc-2, that extends to a radius of 7' (4 kpc). The total inferred H2 mass is 7ï¿½108 Msolar, which is 30% of the total H I mass. We combine the CO data with VLA H I maps to obtain a map of the total gas surface density (Î£HI+Î£H2) in IC 342. The gas surface density shows a centrally peaked disk, dominated by H2 to a radius of 5' (3 kpc). Spiral arms run continuously from the inner to outer galaxy, transitioning smoothly from predominantly molecular in the inner galaxy to predominantly atomic at large radii.